System for controlling fluid flow

ABSTRACT

Embodiments of the present invention provide systems and methods of controlling fluid dispense to ensure clean break off of fluid at the end of a dispense process and to reduce crystallization of fluid in the dispense nozzle. One embodiment of the present invention can include a controller that can, generate a flow control signal to cause a control valve to close according to a first close rate parameter for a first segment of the close range and to generate the flow control signal to cause the control valve to close according to a second close rate parameter for a second segment of the close range.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of dispensingfluids. More particularly, the present invention relates to systems andmethods of controlling fluid flow at the end of a dispense process.

BACKGROUND OF THE INVENTION

The manufacture of semiconductors often requires dispensing variousliquids on a silicon wafer. In Spin-On Glass (“SOG”) methods, a SOGmaterial, typically a silicon dioxide solution, is dispensed by a nozzleonto the center of a silicon wafer. The wafer is then immediatelyrotated at a high speed, spreading the SOG material across the wafer.The amount of SOG material dispensed, surface tension of the SOGmaterial solution, viscosity of the SOG material solution, the oxideconcentration of the SOG material and the spin rate of the wafer affectthe resulting film thickness.

In many semiconductor manufacturing systems, pumps and valves are usedto control the amount of liquid dispensed from the nozzle. During thedispense process, a controller determines how much liquid has beendispensed based on the flow rate of the liquid and the amount of timethe dispense process has been ongoing. When the appropriate amount ofliquid has been dispensed, the controller can signal a control valveupstream of the nozzle to close, cutting off fluid flow to the nozzle. Asuckback valve, also located upstream of the nozzle, can draw fluidremaining in the nozzle out of the nozzle.

In order to achieve proper uniformity of a SOG material layer across awafer, the fluid must break off cleanly with no droplets hitting thewafer after the end of the dispense process. Many semiconductormanufacturing systems use open/close pneumatic valves to terminate adispense process. An open/close valve will typically close with a singlespeed more quickly than desired to produce a clean break off. In otherwords, an open/close valve will typically slam shut when the controllersignals the end of the dispense process. This can cause the fluid toseverely oscillate at the end of the dispense process, potentiallycausing droplets or excess fluid to drip onto the wafer, therebyaffecting the uniformity of film thickness on the wafer.

One solution that has been developed for this problem has been to employproportional valves in which the rate of change of closure (i.e., theacceleration) can be set to a predefined value, such that the valve canclose more slowly than “slamming shut.” One example of such a valve is apneumatic control valve that uses a needle valve to control the pressureat the pneumatic control valve. Based on the state of the needle valve,the rate of closure of the pneumatic control valve is controlled. Inthese systems, a particular acceleration is selected and applied to thecontrol valve such that rate of change of closure is substantiallyconstant as the valve closes. While such systems can reduce droplets ofexcess fluid at the end of the dispense process, they can still allowsome excess fluid to be deposited on the wafer.

Whether an open/close valve or proportional valve with predeterminedrate of closure is employed, prior art semiconductor manufacturingsystems suffer a further deficiency. After the control valve closes, asuckback valve is engaged that pulls remaining fluid up into thedispense nozzle. Drawing the fluid back into the nozzle too quickly canleave droplets in the nozzle. These droplets can crystallize, leading toproblems in the next dispense process.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a system and method ofcontrolling fluid flow that eliminates, or at least substantiallyreduces, the shortcomings of prior art fluid flow control systems andmethods.

One embodiment of the present invention can include a controller thatfurther comprises a processor, a computer readable memory and a set ofcomputer instructions stored on the computer readable memory. Thecomputer instructions can be executable by the processor to generate aflow control signal to close a fluid control valve based on a firstclose rate parameter for a first segment of a close range and generate aflow control signal to close a fluid control valve based on a secondclose rate parameter for a second segment of the close range.

Another embodiment of the present invention can include a computerprogram product comprising a set of computer instructions stored on acomputer readable memory. The set of computer instructions can compriseinstructions executable to generate a flow control signal to close afluid control valve based on a first close rate parameter for a firstsegment of the close range and to generate a flow control signal toclose a fluid control valve based on a second close rate parameter for asecond segment of the close range.

Yet another embodiment of the present invention can include a method ofending a dispense process comprising generating a flow control signal toclose a fluid control valve based on a first close rate parameter for afirst segment of a close range, determining that a second close rateparameter should apply and generating the flow control signal to closethe fluid control valve based on the second close rate parameter for asecond segment of the close range.

Yet another embodiment of the present invention can include a controllerfurther comprising a processor, a computer readable memory and a set ofcomputer instructions stored on the computer readable memory. Thecomputer instructions can comprise instructions executable by theprocessor to determine that a fluid control valve has closed and togenerate a suckback control signal configured to cause a suckback valveto push a fluid to the end of a nozzle.

Yet another embodiment of the present invention can comprise a computerprogram product comprising a set of computer instructions stored on acomputer readable memory, executable by a computer processor, whereinthe set of computer instructions comprise instructions executable todetermine that a fluid control valve has closed and generate a suckbackcontrol signal configured to cause a suckback valve to push a fluid tothe end of a nozzle.

Yet another embodiment of the present invention can include a method fora dispense process comprising determining that a fluid control valve hasclosed and generating a suckback control signal configured to cause asuckback valve to push a fluid to the end of a nozzle.

Embodiments of the present invention provide an advantage over prior artsystems and methods of ending dispense processes by closing a fluidcontrol valve in such a manner that the likelihood that excess fluiddrops will hit a wafer after the end of the dispense process is reduced.

Embodiments of the present invention provide yet another advantage byreducing the crystallization of fluid droplets in a dispense nozzleafter the dispense process has ended.

Embodiments of the present invention provide another advantage byenabling a user to employ any number of techniques using the same set ofcomputer instructions to resolve close control issues for any number ofapplications, including different flow rates, dispense system setups anddispense fluids.

BRIEF DESCRIPTION OF THE FIGURES

A more complete understanding of the present invention and theadvantages thereof may be acquired by referring to the followingdescription, taken in conjunction with the accompanying drawings inwhich like reference numbers indicate like features and wherein:

FIG. 1 is a diagrammatic representation of one embodiment of a fluiddispense system in which embodiments of the present invention can beimplemented;

FIG. 2A illustrates one embodiment of an initial routine for anend-of-dispense process;

FIG. 2B illustrates a mode selection routine according to one embodimentof the present invention;

FIG. 2C illustrates a method for closing a fluid control valve accordingto one embodiment of the present invention;

FIG. 2D illustrates another embodiment of a method for closing a fluidcontrol valve;

FIG. 2E illustrates yet another embodiment of a method for closing afluid control valve;

FIG. 2F illustrates one embodiment of a method of controlling a suckbackvalve;

FIG. 2G is a valve profile graph for a valve closing according to oneembodiment of the present invention;

FIG. 3 is a diagrammatic representation of one embodiment of a dispensesystem;

FIG. 4 is a diagrammatic representation of one embodiment of controller;and

FIG. 5 is a diagrammatic representation of one embodiment of a controlcircuit for a controller.

DETAILED DESCRIPTION

Preferred embodiments of the invention are illustrated in the FIGURES,like numerals being used to refer to like and corresponding parts of thevarious drawings.

Embodiments of the present invention provide systems and methods ofcontrolling fluid dispense to ensure clean break off of fluid at the endof a dispense process and to reduce crystallization of fluid in thedispense nozzle. One embodiment of the present invention can include acontroller that can generate a flow control signal according to a firstclose rate parameter to cause a control valve to close for a firstsegment of the close range and to generate the flow control signalaccording to a second close rate parameter to cause the control valve toclose for a second segment of the close range. The close rate parametercan result in closing the valve at a controlled rate, change in rate, orchange in rate of change. By adjusting the close rate parameters, severeoscillation at the end of the dispense process can be reduced orprevented. Additionally, the controller can generate a suckback controlsignal to cause a suckback valve to push fluid to the end of a nozzle,draw fluid up into the nozzle or assist in cutting of the dispense moresmoothly or more quickly. Because fluid is pushed to the end of thenozzle, the fluid can absorb droplets remaining in the nozzle.

FIG. 1 is a diagrammatic representation of one embodiment of a fluiddispense system 10. Fluid dispense system 10 can include a fluid controldevice 12, flow monitor 14 in fluid communication with control device12, a suckback device 16 in fluid communication with flow monitor 14,and a nozzle 18 in fluid communication with suckback valve 16. Theoutlet of suckback valve 16 can lead to nozzle 18 for dispensing aliquid to a wafer or other object. A controller 20 can be coupled toflow rate monitor 14, fluid control device 12 and suckback device 16 byone or more signal lines.

According to one embodiment of the present invention, fluid controldevice 12 can include any proportional control valve. In other words,fluid control device 12 can include any fluid control valve in which therate of closure can change based on changes in the flow control signalapplied. One embodiment of a proportional fluid control device isdescribed in PCT application PCT/US03/22579, entitled “Liquid FlowController and Precision Dispense Apparatus and System,” (the “LiquidFlow Controller Application”) filed Jul. 18, 2003, which claims priorityof Provisional Application Ser. No. 60/397,053 filed Jul. 19, 2002,entitled “Liquid Flow Controller and Precision Dispense Apparatus andSystem” and is related to U.S. Pat. No. 6,348,098, entitled “FlowController,” filed Jan. 20, 2000 and Provisional Application Ser. No.60/397,162, entitled “Fluid Flow Measuring and Proportional Fluid FlowControl Device”, filed Jul. 19, 2002, each of which is fullyincorporated by reference herein. In the embodiment of the Liquid FlowController Application, the fluid control device, as described inconjunction with FIG. 3, can include a fluid control valve thatregulates fluid flow and a proportional pneumatic control valve thatregulates how quickly and how much the fluid control valve opens orcloses.

During a dispense process, a fluid such as a Spin-On glass fluid,deionized water, photoresist, polyamide, developer, chemical mechanicalpolishing (“CMP”) slurry or other fluid can flow through dispense system10. Flow monitor 14 can measure fluid flow parameters that indicate flowrate (e.g., pressure differential across a restriction, pressure at aparticular sensor or other parameter) and communicate the measurementsto controller 20. Controller 20, according to one embodiment of thepresent invention, can calculate the flow rate of the fluid and, basedon the flow rate of the fluid, the amount of time necessary for apredetermined amount of the fluid to be dispensed. At the end of thedispense process, as determined by controller 20, controller 20 cangenerate a flow control signal to cause fluid control device 12 toclose.

Additionally, controller 20 can generate a suckback control signal tocause suckback device 16 to push fluid into nozzle 18 or draw fluid upnozzle 18. The controller can be configured to generate the suckbackcontrol such that the suckback valve can push fluid to the end of thenozzle and then draw the fluid slowly back into the nozzle. By drawingfluid back into the nozzle at the appropriate speed, residual fluiddroplets in the nozzle can be prevented. Moreover, controller 20 cangenerate the suckback control signal to aid in ending the dispenseprocess. In this embodiment of the present invention, the suckbackdevice can be engage to begin sucking fluid up the nozzle if the fluidcontrol device can not close quickly enough, thereby aiding interminating fluid flow to the wafer.

Controller 20, according to one embodiment of the present invention, cancomprise a processor 22 such as a general purpose processor (e.g., a8051 processor by Intel Corporation of Santa Clara, Calif.), a RISCprocessor (e.g., a PIC 18c452 processor by Microchip Technologies ofChandler, Ariz.) or other processor, a computer readable memory 24(e.g., RAM, ROM, magnetic storage, optical storage, Flash memory)accessible by the processor and computer instructions 25 stored onmemory 24 that are executable by processor 22. According to oneembodiment of the present invention, controller 20 can execute computerexecutable instructions 25 to generate the flow control signal based ona first close rate parameter to cause control device 12 to close with afirst rate of change of closure over a first segment of the valve closerange of the flow control device and to generate the flow control signalto based on a second close rate parameter to cause flow control deviceto close over a second segment of the valve close range. The controllercan switch from generating the flow control signal based on the firstclose rate parameter to generating the flow control signal based on thesecond close rate parameter at a break point. Additionally, controller20 can execute computer executable instructions 25 to generate thesuckback control signal to cause suckback valve to push fluid intonozzle 18 or draw fluid up nozzle 18.

FIGS. 2A–2F are flow charts illustrating various modes of operation fora controller for generating the flow control signal and suckback controlsignal, according to embodiments of the present invention. FIG. 2G is avalve profile graph for an example valve closing according to anembodiment of the present invention. The processes of FIGS. 2A–2F can beimplemented as computer executable instructions stored on a computerreadable memory. For example, the processes of 2A–2F can be implementedas subroutines of a larger control program, portions of the sameprogram, modules of a program or according to any suitable programmingarchitecture as would be understood by those of ordinary skill in theart.

According to one embodiment of the present invention, when thecontroller running a control program determines that a dispense processshould end, the controller can assert an interrupt and enter theend-of-dispense process. During the end-of-dispense process, thecontroller can generate a flow control signal to close the fluid controlvalve according to multiple close rate parameters and can generate thesuckback control signal to cause fluid to be pushed into or drawn up anozzle.

FIG. 2A illustrates one embodiment of an initial routine for anend-of-dispense process. At step 32, the controller can determine thecurrent valve position for the fluid control valve. As would beunderstood by those of ordinary skill in the art, the current valveposition will correspond to the valve position of the control valveduring the dispense process and can be based on a setpoint (e.g., a flowrate set point) asserted to or stored by the controller for regulatingthe dispense process. At step 35, the controller can further calculate avalve close break point. As will be discussed below, the break point cancorrespond to the valve position at which the controller will switchbetween generating a flow control signal based on a first close rateparameter and generating the flow control signal based on a second closerate parameter. The valve break point can be based on the valve closerange (the current valve position determined at step 32 minus the closeor idle valve position) and a predefined break point parameter.

The break point parameter, in one embodiment of the present invention,can be a percentage of the valve close range. As example, if the currentvalve position is 100 units, the end point is 10 units and the breakpoint parameter is 20, the break point range value will be at 18 units(0.20*90), relative to the valve end point. Since the end point forclosing the valve is at 10 units, the break point can have a break pointposition value of 28 units. In other embodiments of the presentinvention, the break point can be a predefined value.

The controller, at step 36, can set a First_Segment Flag to True andreturn to a main control program to initiate a mode selection routine.The First_Segment Flag indicates that the fluid control valve is in thefirst segment of its close range. In other words, the First_Segementflag indicates whether the flow control valve has closed far enough toreach the break point.

If the controller has multiple modes of operation for theend-of-dispense process, the controller can enter a mode selectionroutine, such as that illustrated in FIG. 2B. In the example of FIG. 2B,the controller has five modes of operation. The mode of operation for aparticular dispense process can be predefined, can be asserted by anadministrative system in communication with controller or can beestablished in any manner. In one embodiment of the present invention,the controller can repeat the process for a particular mode of operationuntil the fluid control valve is closed or until the end-of-dispenseinterrupt is no longer asserted.

FIG. 2C illustrates one embodiment of the operation of the controllerunder a first mode of operation (e.g., mode 1 from FIG. 2B). Forpurposes of FIGS. 2C–2F, the close rate parameter is an accelerationparameter that corresponds to the rate of change in the close rateacceleration. In the embodiment of FIG. 2C, the controller, at step 37,can determine a remaining close range for the valve. Continuing with theprevious example in which the valve is initially at 100 units and hasand endpoint of 10 units, the new range for the first iteration of mode1 would be 90 units. In subsequent iterations, as will be discussedbelow, the remaining range can be equal to the value change calculatedat step 40 or step 42 from a previous iteration or can be calculatedbased on a new valve position and the end point.

At step 38, the controller can determine if a First_Segment Flag is trueand, if so, can generate the flow control signal based on a firstacceleration factor. The value change (i.e., the difference between theend point and valve position at the end of the iteration) will be therange determined at step 37 divided by the first acceleration factor(step 40). Using the previous example, and assuming the firstacceleration factor is 10, the value change for the first iteration is 9(i.e., 90/10). If the First_Segment Flag is false, on the other hand,the controller can generate the flow control signal based on the secondacceleration factor. In this case, the value change between the endpoint and the valve position will be the range determined at step 37divided by the second acceleration factor (step 42).

The controller can determine the new valve position (step 44) based onthe value change for the iteration (i.e., the value determined at step40 or step 42) and the valve end point or idle position. Again,continuing with the previous example in which the idle position is 10units and the value change 9, the new valve position is 19 units at theend of the first iteration.

At step 46, the controller can determine if the new valve position isless than the break point position. If the new valve position is lessthan the break point position, the controller, at step 48, can set theFirst_Segment Flag to false. Otherwise, the controller can leave theFirst_Segment Flag as true. Using the previous example, the new valveposition is 19 units and the break point position is 28 units (from FIG.2A), so the First_Segment Flag will be changed to false. The controllercan then exit the routine of FIG. 2C.

If the end-of-dispense flag is still set after a particular iteration,the controller can again enter the routine of FIG. 2C. The controllercan continue iterating through the process of FIG. 2C while theend-of-dispense flag is set. In the next iteration, the range calculatedat step 37 will be the new valve position calculated at step 44 of theprevious iteration minus the endpoint (e.g., 19−10 or 9, in the previousexample). In this case the new range will equal the value changedetermined at step 40 or step 42 of the previous iteration.

It should be noted that as the controller iterates through the processof mode 1 according to the embodiment of FIG. 2C, the valve positionwill approach the end point. If configured to iterate enough times, thedifference between the valve position and endpoint can become so smallthat it can not be detected within the resolution of the controller.Therefore, the controller can continue iterating through the process ofmode 1 until the difference between the new valve position calculated atstep 44 and the end point is below a particular value, and when thedifference is below the predetermined value, can generate a flow controlsignal of sufficient magnitude to ensure that the valve is closed.

FIG. 2D is a flow diagram illustrating one embodiment of the operationof the controller under a second mode of operation (e.g., mode 2 fromFIG. 2B). In mode 2, the controller works in a similar manner as whenthe controller is in mode 1 except that in mode 2 the first accelerationfactor is set such that flow control signal will cause the fluid controlvalve to close as quickly as possible until the break point is reached.After the break point is reached, the controller can generate the flowcontrol signal according to a second acceleration factor such that thefluid control valve will close more slowly.

In the embodiment of FIG. 2D, the controller, at step 50, can determinea remaining range of closure. If it is the first iteration, theremaining range will be the valve position determined at step 32 of FIG.2A minus the end position of the valve. Additionally, the controller, atstep 52, can determine if the First_Segment Flag is set to true. If theFirst_Segment Flag is set to true, the controller can generate the flowcontrol signal such that the fluid control valve will close as quicklyas possible. Accordingly, the controller, at step 54, can determine avalue change (i.e., the difference between the valve position at the endof the iteration and the end point) for a particular iteration based onthe control valve closing as quickly as possible. If, conversely, theFirst_Segment Flag is false, the controller can generate the flowcontrol signal based on the second acceleration factor. In this case,the value change will be the remaining close range divided by the secondacceleration factor (step 56).

The controller, at step 58, can then determine the new position of thevalve, which can equal the valve end point position plus the valuechange determined at step 54 or step 56. At step 60, the controller candetermine if the new position of the valve is less than the break pointposition and, if so, can set the First_Segment Flag to false (step 62).Otherwise, the controller can leave the First_Segment Flag as true. Thecontroller can then exit the routine of FIG. 2D.

If the end-of-dispense flag is still set after a particular iteration,the controller can again enter the routine of FIG. 2D. The controllercan continue iterating through the process of FIG. 2D while theend-of-dispense flag is set until the difference between the new valveposition determined at step 58 and the end position is below aparticular value.

FIG. 2E is a flow diagram illustrating one embodiment of the operationof the controller under a third mode of operation (e.g., mode 3 fromFIG. 2B). In mode 3, the controller works in a similar manner as whenthe controller is in mode 2, except that the controller will generatethe flow control signal to close the fluid control valve according to afirst acceleration factor for a first segment of the close range andwill generate the flow control signal to close the valve as quickly aspossible over a second segment of the close range.

In the embodiment of FIG. 2E, the controller, at step 64 can determine aremaining range of closure. If it is the first iteration, the remainingrange will be the valve position determined at step 32 of FIG. 2A minusthe end position of the valve. Additionally, the controller, at step 66,can determine if the First_Segment Flag is set to true. If theFirst_Segment Flag is set to true, the controller can generate the flowcontrol signal according to a first acceleration factor. In this case,the value change will be the remaining close range from step 64 dividedby the first acceleration factor (step 68). If, however, theFirst_Segment Flag is false, the controller can generate the flowcontrol signal based on the second acceleration factor that causes thefluid control valve to close as quickly as possible. The controller, atstep 70, can therefore determine a value change (i.e., the differencebetween the valve position at the end of the iteration and the endpoint) for a particular iteration in which the First_Segment Flag isfalse based on the control valve closing as quickly as possible.

The controller, at step 72, can then determine the new position of thevalve, which can equal the valve end point position plus the valuechange determined at step 68 or step 70. At step 74, the controller candetermine if the new position of the valve is less than the break pointposition and, if so, can set the First_Segment Flag to false (step 76).Otherwise, the controller can leave the First_Segment Flag as true. Thecontroller can then exit the routine of FIG. 2D.

If the end-of-dispense flag is still set after a particular iteration,the controller can again enter the routine of FIG. 2D. The controllercan continue iterating through the process of FIG. 2D while theend-of-dispense flag is set until the difference between the new valveposition determined at step 58 and the end position is below aparticular value.

In the fourth mode of operation (e.g., mode 4 from FIG. 2C), thecontroller can generate a fluid control signal to close the fluidcontrol valve as quickly as possible or according to a particularacceleration factor. Thus, the fluid control valve can “slam shut” orclose according to a particular acceleration factor.

FIG. 2F is a flow diagram illustrating one embodiment of the operationof the controller under a fifth mode of operation (e.g., mode 5 fromFIG. 2B). In mode 5, the controller, according to one embodiment of thepresent invention, can generate a flow control signal to cause the fluidcontrol valve to close as quickly as possible (step 78). Once the fluidcontrol valve has closed, whether done as quickly as possible accordingto step 78 or done according to multiple acceleration factors, thecontroller can generate a suckback control signal to cause the suckbackvalve to push fluid into the dispense nozzle (step 82). The controllercan be empirically calibrated for a particular system set up and fluidto generate the suckback control signal such that the suckback will pushthe fluid to the end of the nozzle, without dispensing the fluid fromthe nozzle. The controller can then generate the suckback control signalto cause the suckback valve to draw the fluid back into the nozzleaccording to any suckback control scheme known in the art (step 84). Thecontroller can be empirically calibrated to draw the fluid back into thenozzle slowly enough to prevent residual droplets forming in the nozzle.This calibration can be based, for example, on the dispense processsetup, nozzle configuration and fluid being dispensed.

It should be noted that although FIGS. 2A–2F were discussed in terms ofseparate software routines, the processes of FIGS. 2A–2F can beimplemented as portions of the same program, modules of a program,objects or according to any suitable programming language andarchitecture. It should be further noted that the controller can beconfigured to operate according to each of the modes, all of the modesor any combination of the modes discussed in conjunction with FIGS.2A–2F. Moreover, FIGS. 2A–2F are provided by way of example and are notintended to limit the manner in which the controller can generate theflow control signal according to multiple acceleration factors.

While the close rate parameter in the examples of FIGS. 2C–2D is anacceleration factor that causes the rate of change of closing (i.e., theclose rate acceleration) to change at different rates over the firstsegment and second segment of the close range, embodiments of thepresent invention can also be configured such that the close rateparameter corresponds to a particular close rate. In this case, thefluid control valve can close according to a first close rate for afirst segment of the close range and close with a second close rate fora second segment of the close rate. Additionally, the close rateparameter can correspond to a particular rate of change in close rate(i.e., close rate acceleration), such that the valve can close with afirst close rate acceleration for a first segment of the close rate andclose with a second close rate acceleration for a second segment of theclose rate.

FIG. 2G illustrates a valve close profile for an example valve closingaccording to one embodiment of the present invention. The x axisrepresents time and the y axis represents the pressure differential(measured in volts) detected by one or more pressure sensors. As theflow rate of a fluid is proportional to the pressure difference, thepressure difference indicates the amount the fluid control valve hasclosed.

In the example of FIG. 2G, the controller can determine, at point 85,that a dispense process should end. For a first segment of the valveclose range, (e.g., until break point 86), the controller can generate aflow control signal to close the flow control valve according to a firstclose rate parameter, resulting in the decrease in flow rate representedin the graph between point 85 and 86. For a second segment of the closerange (e.g., after the valve has closed to or beyond break point 86),the controller can generate the flow control signal based on a secondclose rate parameter. When the valve has closed (represented at point87), the controller can generate the flow control signal required tokeep the flow control valve closed.

Thus, embodiments of the present invention can generate a flow controlsignal according to various close rate parameters to cause a fluidcontrol valve (such as that in fluid control device 12 of FIG. 1). Thecontroller can generate the flow control signal based on a first closerate parameter for a first segment of the close range (e.g., for a firstrange of closure of the fluid control valve) to cause a fluid controlvalve to close with a first close rate, close rate acceleration, or rateof change in close rate acceleration and can further generate the flowcontrol signal based on a second close rate parameter for a secondsegment of the close range to cause the fluid control valve to closewith a second close rate, close rate acceleration, or change close rateacceleration. The controller can switch between basing the flow controlsignal on the first close rate parameter and the second close rateparameter at a break point.

It should be noted that the first close rate parameter, second closerate parameter and break point can be defined for a particular dispenseprocess and system. These parameters can vary according to the fluidproperties, of the fluid being dispensed, particularly the surfacetension and viscosity, the dispense system configuration, the rate atwhich the fluid will be dispensed and the application for which thedispense process is being used. Empirical testing and calibration can beused to determine the first close rate parameter, second close rateparameter and break point that reduce the potential for excess fluidbeing deposited on the wafer for the particular dispense process.

It should be further noted that embodiments of the present invention canalso apply additional close rate parameters. For example, a controllercan execute computer instructions to generate a fluid control signalbased on a first close rate parameter for a first segment of the fluidcontrol valve close range, generate the fluid control signal based on asecond close rate parameter for a second segment of the close range ofthe fluid control valve and generate the fluid control signal based on athird close rate parameter for a third segment of the fluid controlrange and so on. The controller can automatically switch betweengenerating the fluid control signal on the various close rate parametersat one or more predefined breakpoints. Thus, the controller can generatean arbitrarily complex closing profile for the fluid control valve.

Additionally, the controller can cause the suckback valve to assist inthe end of dispense control to determine the fluid height at the end ofthe dispense proces. The controller can be configured to cause thesuckback valve to begin moving fluid at a point defined sometime duringthe dispense (e.g., from 0% to 50% of dispense time prior to the end ofdispense or other time). The moving fluid can push fluid to the end ofthe nozzle or pull fluid up into the nozzle as defined by the controllerconfiguration.

FIG. 3 is a diagrammatic representation of one embodiment of a fluidcontrol system in which embodiments of the present invention can beimplemented. A fluid control device 90 is shown having a liquid inletline 92 and a liquid outlet line 93 for ultimate dispensing of theliquid to a point of use, such as a substrate which can be a wafer (notshown). Fluid control device 90 can include a fluid control valve 94,such as that described in the Liquid Flow Control Application, and apneumatic proportional control valve 96, pneumatically connected tofluid control valve 94. The liquid outlet line 93 is in fluidcommunication with a frictional flow element 97, such that all of theliquid exiting the fluid control device 90 enters the frictional flowelement 97. A first pressure sensor 98 such as a pressure transducer,which can be integral with the fluid control device 90 housing, ispositioned at or near the inlet of the frictional flow element 97 (suchas at or near the outlet of the fluid control valve 94) to sense a firstpressure, and a second pressure sensor 100 such as a pressure transduceris positioned at or near the outlet of the frictional flow element 97 tosense a second pressure. Alternatively, a single differential pressuresensing device could be used. The portion of the pressure sensor(s) thatcontact the fluid is preferably made of an inert material (with respectto the fluid used in the application) such as sapphire, or is coatedwith a material compatible with the fluids it contacts, such asperfluoropolymer. The sensors sense pressure and temperature in thefluid path, and send signals indicative of the sensed pressure andtemperature to a controller.

Each pressure sensor 98, 100 (or a single differential pressure sensingdevice) is in communication with a controller 102, such as a controllerhaving proportional, integral and derivative (PID) feedback components.As each sensor 98 and 100 samples the pressure and temperature in itsrespective fluid line, it sends the sampled data to the controller 102.The controller 102 can compare the values and calculate a pressure dropacross the frictional flow element 97. A signal from the controller 102based on that pressure drop is sent to the pneumatic proportionalcontrol valve 96, which modulates the fluid control valve 94accordingly, preferably after compensating for temperature, and/orviscosity and/or density.

More specifically, the system preferably is calibrated for the fluidbeing dispensed using a suitable fluid such as deionized water orisopropyl alcohol as a fluid standard. For example, once the system iscalibrated to the standard, preferably experimentally, thecharacteristics of the fluid to be dispensed are inputted or determinedautomatically, such as viscosity and density, so that the fluid to bedispensed can be compared to the standard and a relationshipestablished. Based upon this relationship, the measured pressure drop(as optionally corrected for temperature, viscosity, etc.) across thefrictional flow element, is correlated to a flow rate, compared to thedesired or target flow rate, and the fluid control valve 94 is modulatedaccordingly by the pneumatic proportional control valve 96.

A suckback device, that preferably includes programmable proportionalvalve 104, is in communication with a proportional control valve (whichcan be the same or different from pneumatic proportional control valve96) and is controlled by the controller (or by a different controller).It is actuated when fluid dispense is stopped or in transition, pushingfluid into the dispense nozzle, thereby reducing or eliminating theformation of undesirable droplets that could fall onto the wafer whenthe fluid dispense operation is interrupted, and drawing the fluid backfrom the dispense nozzle to minimize or prevent its exposure toatmosphere. The rate and extent of the suckback valve 104 opening andclosing is controlled accordingly. Preferably the suckback valve 104 islocated downstream of the fluid control valve 94.

By controlling the pressure to the fluid control valve 94 by, forexample, controlling pneumatic proportional control valve 96, variousfluid dispensing parameters can be controlled. For example, where theliquid to be dispensed is a low viscosity liquid, the fluid controlvalve 94 can be carefully modulated using pressure to ensure uniformdispensing of the liquid.

Additionally, the rate at which fluid control valve 94 closes can beregulated. By changing the rate of closure of fluid control valve 94,drops of excess fluid at the end of the dispense process can be reducedor prevented. Once the pressure-to-volume relationship of the particularfluid control valve 94 being used is characterized, unlimitedflexibility can be obtained.

The embodiment illustrated in FIG. 3 is simply one embodiment of adispense system in which embodiments of the present invention can beimplemented. The fluid control device of FIG. 3 (e.g., fluid controlvalve 94 and proportional pneumatic control valve 96) can be responsiveto a fluid control signal to close the fluid flow path. The fluidcontrol signal can be based on one or more close rate parameters, asdiscussed in conjunction with FIGS. 2A–2E. Additionally, the suckbackcontrol device can be responsive to a suckback control signal to pushfluid into a dispense nozzle or draw fluid into the nozzle as describedin conjunction with FIG. 2F.

FIG. 4 is a block diagram that illustrates one embodiment of acontroller 102 that can generate a fluid control signal to throttle/opena pneumatic proportional control valve (e.g., pneumatic proportionalcontrol valve 96 of FIG. 3), which will in turn cause fluid controlvalve (e.g., fluid control valve 94 of FIG. 3) to open or close.Controller 102 can include a power supply 105, a house keeping processor106, a pressure circuit 108, an auxiliary function circuit 110, acontrol valve driver 112, a suckback valve driver 114, a comportinterface 116, an I/O circuit 118 and a control processor 120. Controlprocessor 120 can include flash memory 122 that can store a set ofcomputer readable instructions 124 that are executable to generate aflow control signal based on pressure signals received from the pressurecircuit. The flow control signal can be generated according to anyscheme for generating valve control signals known or developed in theart. Various components of controller 102 can communicate through databus 126. A supervisor unit 128 can monitor various functions ofcontroller 102. It should be noted that while computer readableinstructions 124 are shown as software at a single memory, computerreadable instructions can be implemented as software, firmware, hardwareinstructions or in any suitable programming manner known in the art.Additionally, the instructions can be distributed among multiplememories and can be executable by multiple processors.

In operation, power supply 105 can provide power to the variouscomponents of controller 102. Pressure circuit 108 can read pressuresfrom upstream and downstream pressure sensors and provide an upstreamand downstream pressure signal to control processor 120. Controllerprocessor 120 can calculate a flow control signal based on the pressuresignals received from pressure circuit 108 and control valve driver 112,in turn, can generate a drive signal based on the flow control signal.The generation of the flow control signal can occur according to themethodology discussed in the Liquid Flow Controller Application oraccording to any control signal generation scheme known in the art. Atthe end of the dispense process, the controller can generate the flowcontrol signal based on various close rate parameters as discussed inconjunction with FIGS. 2A–2E. Additionally, the controller can generatea suckback control signal as discussed in conjunction with FIG. 2F. Themethodologies for generating the flow control signal and the suckbacksignal can be implemented as software, or other computer readableinstructions (e.g., instructions 124), stored on a computer readablememory (e.g., RAM, ROM, FLASH, magnetic storage or other computerreadable memory known in the art) accessible by control processor 120.

With respect to other components of controller 102, house keepingprocessor 106 can be a general purpose processor that performs a varietyof functions including directing communications with other devices orany other programmable function, known in the art. One example ofgeneral purpose processor is an Intel 8051 processor. Auxiliary functioncircuit 110 can interface with other devices. Suckback valve driver 114can control a suckback valve (e.g., suckback valve 104 of FIG. 1).Comport interface 116 and I/O circuit 118 can provide various means bywhich to communicate data to/from controller 102. Additional componentscan include a supervisor unit 2720 that can perform device monitoringfunctions known in the art, various eeproms or other memories,expansions ports or other computer components known in the art.

FIG. 5 is a block diagram that illustrates one embodiment of the controllogic circuit of controller 102 that can generate a valve drive signalto throttle/open a proportional control valve. Several of the componentsof controller 102 are illustrated including control processor 120,comport interface 116 and supervisor unit 128. Additionally, anexpansion port 130 is shown. Expansion port 130 can be used to adddaughter boards to expand the functionality of controller 102.

In the embodiment of FIG. 5, the functionality of house keepingprocessor 106 is split into three portions: processing portion 132,memory device portion 134 and dual port RAM portion 136. Memory deviceportion 134 can include various memories including Flash Memory, RAM,EEPROM and other computer readable memories known in the art. Oneadvantage of providing Flash Memory to house keeping processor 106 isthat it allows easy downloads of firmware updates via, for example,comport interface 116. Additionally memory device portion 134 caninclude functionality for chip selections and address decoding. Itshould be noted that each of memory device portion 134, dual port RAMportion 136 and processing portion 132 can be embodied in a singleprocessor. Control processor 120 and processing portion 132 of the housekeeping processor can share data, in one embodiment of the presentinvention, through mutual access to dual port RAM portion 136. Controlprocessor 120 and processing portion 132 of the house keeping processorcan be driven by a single system clock 138 (e.g., a 20 MHz clock) ordifferent system clocks.

Control processor 120 can include flash memory 122 that can store a setof computer executable instructions 124 that are executable to generatea flow control signal based on pressure signals received from thepressure circuit according to the control scheme described in the LiquidFlow Controller Application. Additionally, control processor 120 canexecute instructions 124 to generate a flow control signal according tovarious close rate parameters to cause a fluid control valve (such asfluid control valve 94 of FIG. 3) to close. The controller can generatethe flow control signal based on a first close rate parameter for afirst segment of the close range and can further generate the flowcontrol signal to cause the fluid control valve to close according to asecond close rate parameter for a second segment of the close range. Thecontroller can switch between basing the flow control signal on thefirst close rate parameter and the second close rate parameter at abreak point. By calibrating the close rate parameters for a particularfluid and dispense systems, embodiments of the present invention canprevent excess drops of fluid from falling onto a wafer after thedispense process has ended.

Control processor 120 can also execute instructions 124 to generate asuckback control signal configured to cause a suckback valve to pushfluid to the end of a dispense nozzle and then draw the fluid back intothe nozzle. As the fluid is pushed to the end of the dispense nozzle,the fluid can absorb fluid droplets remaining in the nozzle. The fluidcan then be drawn back into the nozzle to prevent air flow around thenozzle from causing crystallization of the fluid. The fluid can be drawnback slowly enough to prevent droplets of excess fluid from remaining inthe nozzle.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and tat the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed in the following claims.

1. A system for regulating fluid flow comprising: a controller furthercomprising: a processor; a computer readable memory; a set of computerinstructions stored on the computer readable memory, the computerinstructions comprising instructions executable by the processor to:generate a flow control signal to close a fluid control valve based on afirst close rate parameter for a first segment of a close range; andgenerate a flow control signal to close the fluid control valve based ona second close rate parameter for a second segment of the close range,wherein the first close rate parameter is a first acceleration factorcorresponding to a first rate of change in a close rate acceleration andthe second close rate parameter corresponds to a second rate of changein the close rate acceleration.
 2. The system of claim 1, wherein thecomputer instructions further comprise instructions executable todetermine if a valve position is less than a break point.
 3. The systemof claim 1, wherein the computer instructions further compriseinstructions executable to generate a suckback control signal to cause asuckback valve to push fluid into a nozzle.
 4. The system of claim 1,further comprising: a fluid control device coupled to the controllercomprising the fluid control valve; a suckback valve coupled to thecontroller in fluid communication with the fluid control device; andwherein the fluid control device is responsive to the flow controlsignal to close the fluid control valve.
 5. The system of claim 4,wherein the fluid control device comprises the fluid control valve and aproportional pneumatic control valve.
 6. The system of claim 5, whereinthe proportional pneumatic control valve is responsive to the flowcontrol signal, and wherein the proportional pneumatic control valvecloses the fluid control valve by applying pneumatic pressure to thefluid control valve.